1. Field of the Invention
This invention relates generally to structural members particularly useful for railed transportation systems. More particularly, the invention relates to a hollow structural members, a rail system based thereon and methods of manufacturing such hollow structural members.
2. Description of Related Art
Railed transportation systems are well known in the art. Most conventional railways for transportation of people, goods and other resources rely on friction between the drive wheels and rails. Such conventional rail transportation systems may not be suitable for use on steep grades where traction may become a problem. To compensate for the lack of necessary friction, various elaborate multiple-wheeled and spring-loaded friction-based rail transportation systems have been devised, such as those described in U.S. Pat. No. 4,602,567 to Hedström, U.S. Pat. No. 5,069,141 to Ohara et al., U.S. Pat. No. 5,231,933 to DiRosa, U.S. Pat. No. 5,419,260 to Hamilton, U.S. Pat. No. 5,964,159 to Hein, U.S. Pat. No. 6,053,286 to Balmer, U.S. Pat. No. 6,666,147 to Minges and U.S. Patent Application Publication No. 2004/0168605 to Minges. However, these systems are inherently complex mechanical systems.
For applications where steep grades are the norm, railed transportation systems may rely on a toothed rack rail, usually between the running rails in a system known variously as a “cog railway”, a “rack-and-pinion railway” or simply, “rack railway”. Trains operated on a rack railway are generally fitted with one or more cog wheels or pinions that mesh with the rack rail for driving the train along the track. However, such rack railway systems suffered from derailments when the cog wheel slipped out of the teeth in the rail rack. Additionally, the rail rack itself was expensive to produce and maintain. Furthermore, switches for rack railways were more complex because of the rail rack.
In other approaches to driving over steep gradients, railed transportation systems may rely on other drive mechanisms such as cables and chain-driven systems to pull a car up a track, or to lower it down a track on a steep incline. Examples of conventional cable-driven, railed transportation systems include U.S. Pat. No. 3,891,062 to Geneste, U.S. Pat. No. 4,026,388 to Creissels, U.S. Pat. No. 4,534,451 to Peter, U.S. Pat. No. 4,821,845 to DeVaiaris and U.S. Pat. No. 6,739,430 to Hill. A variation on the cable-driven systems are those which utilize a chain-drive mechanism such as that disclosed in U.S. Pat. No. 1,838,204 to Wood and U.S. Pat. No. 4,627,517 to Bor. While these cable and chain-driven systems tend to be simpler than the friction-based systems for inclined applications, they do not lend themselves well to applications that include turns and changes in inclination because of the nature of cable and chain-driven drives. More specifically, it is difficult to configure a chain or cable for driving a car over a track having turns and changes in inclination because the force exerted by a chain or cable is linear in nature.
Thermal expansion of steel and other track materials has been a limiting factor for simple track design for many years. For example, in the intermountain west, a 120° F. temperature differential may result in approximately one inch of track expansion per 100′ of track. If such expansion is not accounted for through stronger reinforcements and supports, the result can be bowing or buckling of the track due to thermal expansion. For this reason, track lengths have been limited to short lengths in most conventional elevator and funicular equipment applications.
One method of dealing with track expansion is to capture the expansion between structural members. This method requires the use of larger foundations and structural members for the track supports to withstand the stresses built up between captured points of the track. This thermal expansion results in a deflection of the track between the captured points. This deflection may cause the track to bend, twist, or at worst case, buckle the track or supports, all of which are undesirable. The deflection also causes additional stresses to all connections including fasteners and connection brackets and/or weldment points requiring the strengthening of these connections. Over time with the increase in thermal cycles, the potential for premature failure of these connection or weldment locations generally increases, resulting in an undesirable failure. The design, manufacturing and installation costs for both labor and materials to compensate for this thermal expansion all increase as a result. For these reasons, the reinforcement method is not preferred as it creates considerable design challenges and increases the economic cost to the system.
Another approach to solving the thermal expansion problem in tracks relies on low-friction clamping systems. The low-friction clamping system allows the track to expand and contract while keeping the track constrained at the supports. For example, this method can utilize dissimilar materials in the clamp, or a roller and bearing assembly. This approach requires a low enough coefficient of friction to allow movement of the track while remaining constrained. A low-friction clamping system is susceptible to contamination and requires additional maintenance to ensure free movement in the track system. This method, while achieving a desired result for reducing the stresses in a long track system, is complicated and requires significant maintenance for long-term operation. For these reasons, the low-friction clamping system approach is not preferred because of the additional maintenance and expense to operate such an intricate system.
Thus, there is a need in the art for a modular track or rail system that can traverse an unlimited track length. It would be advantageous if the track were formed from a plurality of lightweight hollow structural members. It would also be advantageous to have a rail system that is not limited by inclination of the terrain over which it is constructed. It would also be advantageous to have a rail system that is virtually unlimited in curvature of the track. It would also be advantageous to have a rail system that can compensate for thermal expansion without resorting to the additional expense and maintenance of the reinforced support or low-friction clamping methods of the prior art.